Pressure control of electrode position in gas tube



June 23, 1970 R. A. ECKEL PRESSURE CONTROL OF ELECTRODE POSITION IN GAS T UBE Filed Oct. 25. 1967 INVENTOR ROBERT A. E'CKEL ATTORNEY United States Patent US. Cl. 313146 2 Claims ABSTRACT OF THE DISCLOSURE A short-arc, compact, high pressure lamp utilizing a bellows to control the inter-electrode arc spacing, which control allows a minimum or optimum electrode separation distance while starting the lamp and provides for standard arc length during normal operation.

The invention relates to electrical discharge lamps and more particularly to high pressure, high current, gas or vapor discharge short-arc lamps. These lamps have a field of utility in optical communication systems, for example.

Lamps of the short-arc type are known to the prior art, and in general are constructed of an envelope composed of a material capable of withstanding high temperatures while providing a chamber for gases such as argon, xenon, neon, etc., alone or with mercury or other vapor additives, and within which are located electrodes for providing an arc. Such lamps are normally shaped to provide a central bulbous section within which the cathode and anode electrodes are situated. One problem continually encountered with short-arc high pressure lamps is the extremely high voltage necessary to initiate the are discharge. Various designs and structures have been developed over the past years to reduce the initial voltage requirement. However, each configuration appears to have its own inherent limiting application characteristics.

Accordingly, an object of the present invention is to develop a gas discharge lamp with a low starting voltage. Another object is to provide a gaseous discharge lamp with a variably spaced electrode gap. Another object of this invention is to provide a gas discharge lamp having a low starting voltage by the inclusion of .a variably spaced electrode gap which allows initiation of the arc while electrode separation is minimal, but permits normal operation while the electrodes are at a standard arc separation. The invention consists of a gas discharge lamp which has two electrodes relatively arranged in an enclosed gaseous medium. The first electrode is supported so it may be moved relative to the second electrode by a pressure responsive bellows. As the temperature of the gaseous medium is increased during operation by reason of the electric arc discharge in the lamp, the increased pressure due to the higher temperature of the gas causes the bellows to collapse slowly, thereby withdrawing said first electrode to a normal operating position from an initial position closely adjacent said second electrode.

Other and more detailed objects of the invention will become apparent from a better understanding of the invention, which may be had from the accompanying drawing and description thereof.

The figure shows a view, partly in section, of one embodiment of the present invention.

Referring to the figure, the discharge lamp has an envelope which may be constructed of clear fuzed quartz to provide strong wall structure for withstanding the high temperatures and pressures encountered during operation. The envelope 10 encloses cathode 14 and anode 16 in a gaseous medium 12. The cathode 14 and anode 16 may be constructed of tungsten rod, and the 3,517,248 Patented June 23 1970 gaseous medium 12 may be argon, xenon, neon, etc., alone or with mercury or other vapor additives. Annular collars 18, 20 and 24 support the electrodes in position, and the discharge lamp as a whole has end structures 22 and 34 for support and connection. Reference may be made to Beese, U. S. Pat. No. 3,315,116, for particular details in regard to this structure.

The particular structure for relatively displacing the electrodes 14 and 16 is shown by bellows 26. Bellows 26 is joined to cathode 14 at plate element 30, and element 28 supports the bellows in a centralized position and also cooperates with end stops 32 to maintain the two electrodes with a standard are gap during normal operation of the discharge tube after collapse of the bellows. Before initiation of the electric discharge lamp, the optimum minimum electrode arc gap distance is maintained by contact between elements 30 and 24 via stop means 31 positioned therebetween. Electrode 14 is illustrated respectively at its minimum and maximum arc gap positions by numerals 36 and 38.

The operation will now be described. Before initiating the arc, pressure in both the lamp body and the bellows are nearly equal, with possibly a slightly higher differential in favor of the bellows. After initiation of the the arc, the current discharge increases the temperature of the gas which in turn increases the gas pressure. This increased gas pressure slowly collapses the bellows to bring the arc gap to its normal operating distance.

Although the embodiment in the figure shows the cathode as being displaced relative to the stationary anode, the cathode might be made stationary with the anode movable relative to it. Yet another possibility is to have both electrodes arranged to be displaceable relative to a stationary housing. The bellows shown in the embodiment illustrated in the drawing is basically pressure sensitive, [but the invention as a unit may be viewed as being a temperature sensitive instrument since it is the increase in temperature of the gas which ultimately causes the pressure differential. In any event, any suitable parameter subject to change during operation of the lamp may be utilized to relatively displace the electrodes. However, the preferred embodiment is pressure responsive as illustrated in the drawing.

Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. A short-arc, high pressure lamp comprising:

a sealed envelope;

at temperature responsive gaseous medium enclosed within said envelope, said gaseous medium increasing its pressure in response to an increase in temperature;

a first electrode supported within said envelope;

a second electrode supported within said envelope;

means responsive to a change in pressure of said gaseous medium for displacing said first electrode relative to said second electrode from a first position closely adjacent said second electrode at initiation of said lamp to a second position more remote from said second electrode than said first position, said second position being the normal operating position of said first electrode, with the result that a lower initiation voltage is required to start said lamp, said pressure responsive displacing means comprising a bellows having its exterior in communication with the interior of said envelope and its interior in communication with the exterior of said envelope so as to be responsive to a pressure dillerential therebetween.

3 4 2. The lamp of claim 1 wherein: 2,839,701 6/1958 Bourns 313146 said lamp includes stop means to limit the travel of 3,229,145 1/ 1966 Jensen 313-146 said first electrode Within said tube to said first posi- 3,244,000 4/1966 Ballard 313146 X tion for initiation of said tube and to said second 2,786,955 3/1957 Trolan 313-147 X position for normal operation of said tube. 6 3,452,236 6/ 1969 Beese 313l46 X References Cited ROBERT SEGAL, Primary Examiner UNITED STATES PATENTS U,S CL X,R, 2,441,284 5/1948 Parrish 313146 X 214 2,751,786 6/1956 Coulbourn et al. 313-146 X 10 

